To increase spectrum usage efficiency, in wireless communications, modulation signals of a plurality of different standards, for example, OFDM (Orthogonal Frequency Division Multiplexing), CDMA (Code Division Multiple Access), and TDMA (Time Division Multiple Access) are used. However, using OFDM as an example, a signal of OFDM has a relatively high peak-to-average ratio, and therefore, OFDM has a relatively high requirement on a power amplifier of a base station. To amplify, without distortion, these signals having a high peak-to-average ratio, the power amplifier of the base station may use two manners. One manner is power back-off, that is, an operating state of the power amplifier is set to a class A or a class AB. However, because a feature of a power amplifier transistor is limited, this manner causes efficiency of the power amplifier to decrease sharply, and in a case of same output power, causes the base station to consume more energy. The other manner is a high-efficiency power amplifier technology. In this manner, not only relatively high efficiency of the power amplifier can be achieved, but also linearity of the power amplifier can meet a requirement of a related protocol.
Currently, high-efficiency power amplifier technologies commonly used in the industry may include a Doherty technology and an ET (envelope tracking) technology, and specifically may be classified into the following three types:
1. High-efficiency power amplifier technology based on a conventional ET power amplifier. As shown in FIG. 1, generally the ET power amplifier may include one envelope modulator and one class-AB power amplifier. The envelope modulator generates an envelope voltage to replace a fixed voltage to supply power to the power amplifier, so as to perform envelope tracking on the power amplifier, so that the power amplifier is always in a near-saturation operating state, and back-off operating efficiency is increased.
However, overall operating efficiency of the ET power amplifier is equal to a product of operating efficiency of the envelope modulator and operating efficiency of the power amplifier, and the operating efficiency of the envelope modulator is impossible to reach 100%. Therefore, there is an efficiency loss. In particular, when a modulation signal has a high peak-to-average ratio, due to a limitation of the power amplifier, it is very difficult for the back-off efficiency to reach very high. In addition, once the envelope voltage is excessively low, a gain of a power tube is reduced sharply, and PAE (power added efficiency) is also further reduced. Consequently, this manner has a poor power amplifier effect and poor power amplifier performance.
2. High-efficiency power amplifier technology based on a Doherty ET power amplifier with independent feed. As shown in FIG. 2, the Doherty ET power amplifier may include an envelope modulator, a Doherty main power amplifier, and a Doherty auxiliary power amplifier (that is, a peak power amplifier). The envelope modulator is connected to the main power amplifier, to perform envelope tracking on the main power amplifier, and power is supplied to the auxiliary power amplifier by using a fixed voltage, so that back-off efficiency of a signal having a high peak-to-average ratio can be increased by using an advantage of back-off efficiency of the Doherty power amplifier.
However, a larger ratio of a voltage of the Doherty main power amplifier to a voltage of the Doherty auxiliary power amplifier indicates higher asymmetry of Doherty power amplifier, and a larger dent of power amplifier efficiency. Therefore, in this manner, an efficiency increase is limited, and a very high voltage cannot be configured for the Doherty auxiliary power amplifier due to impact of a breakdown voltage of a power tube. Therefore, there is a problem that saturation power of the power amplifier cannot be further increased. Consequently, this manner also has a poor power amplifier effect and poor power amplifier performance.
3. High-efficiency power amplifier technology based on a Doherty ET power amplifier with separate feed. As shown in FIG. 3, in this case, the Doherty ET power amplifier may include an envelope modulator, a Doherty main power amplifier, and a Doherty auxiliary power amplifier. The envelope modulator is connected to both the main power amplifier and the auxiliary power amplifier, to separately perform envelope tracking on the Doherty main power amplifier and the Doherty auxiliary power amplifier, so that back-off efficiency of a signal having a high peak-to-average ratio can be increased by using an advantage of back-off efficiency of the Doherty power amplifier.
However, at different voltages, a signal of a Doherty main power amplifier link and a signal of a Doherty auxiliary power amplifier link have different phases. Therefore, a phase of a Doherty power amplifier is not optimal at different envelope voltages. Consequently, this manner has a relatively poor power amplifier effect and poor power amplifier performance.
In conclusion, the existing high-efficiency power amplifier technology has problems such as a relatively poor effect and poor performance. Therefore, a new power amplifier technology is urgently needed to resolve the foregoing problems.